While it has been clearly demonstrated that the cerebellum is involved in motor and associative learning, it is remains unclear where and how this learning takes place within the cerebellum. Many studies have focused on the synaptic physiology and electrophysiological properties of Purkinje cells, but very few studies have investigated the role of deep cerebellar nuclear (DCN) neurons in the cerebellar circuit. Behavioral studies of eyelid conditioning have suggested that at least a portion of cerebellar learning takes place or is stored outside the cerebellar cortex, likely in the DCN. However, little is known about the properties of excitatory synapses in the DCN and there has been no direct evidence of synaptic plasticity at this site. This work will provide insight on the function of excitatory synapses in the DCN by making a more detailed study of the basic properties of these synapses than has been done previously. We will begin by investigating the kinetics, pharmacological sensitivity, and voltage dependence of EPSCs, as well as the short-term plasticity of EPSCs during trains of high frequency stimulation. This information will help in understanding how information is transmitted and processed at excitatory synapses in the DCN. In addition, we will investigate whether long-term plasticity is possible at excitatory synapses in the DCN, and if so, the conditions and mechanisms that produce potentiation or depression of EPSCs. These data will provide insight on how information is processed and stored by the cerebellum and in the DCN in particular. [unreadable] [unreadable]